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Nick Kyrgios has responded in brutal fashion to some advice from Australian tennis coach Roger Rasheed.

The 21-year-old was on Monday (AEST) criticised for having a poor preparation for the US Open, which ultimately led to his retirement from a hip flexor injury in his third round match against Ukrain's Illya Marchenko.

Rasheed said Kyrgios sabotaged his own tournament by entering the doubles draw, despite carrying his hip flexor injury into the tournament.

The former coach of Gael Monfils and Grigor Dimitrov said a coach could have drilled some sense into Kyrgios not to play in the doubles draw and instead use his rest days in the singles draw to properly recover and treat his hip complaint.

He laughed off Australian Olympic team chef de mission Kitty Chiller's criticism by attacking her results in the modern pentathlon at the Sydney 2000 Olympics.

"Ha ha she came 14th I don't think that counts as competing in the Olympics," Kyrgios tweeted.

Rasheed on Tuesday told Sky Sports Radio's Big Sports Breakfast he remains a fan of Kyrgios and believes he is an enormous talent "that could be anything".

Kyrgios also posted an image of himself playing basketball with fellow tennis stars Monfils, Bernard Tomic and Lucas Pouille in New York, just two days after withdrawing from Flushing Meadows with a hip injury.

Aussie Lleyton Hewitt has defended Kyrgios over his conduct in New York, hitting back at McEnroe for is accusatory comments.

The Davis Cup captain said Kyrgios may well have quit the US Open much earlier had his third-round match not been played on tennis's biggest stage.

Former tennis great and now commentator McEnroe challenged Kyrgios to quit the sport if his heart wasn't in it before the 21-year-old retired with a hip injury while trailing Illya Marchenko two sets to one on Saturday night (Sunday NZT).

But Hewitt, who is sweating on Kyrgios being fit for Australia's Davis Cup playoff with Slovakia in Sydney next week, says McEnroe is being too harsh.

"It's unfair," he said.

"He was obviously playing with an injury and I know before the first round that he did have a small hip problem that he actually did two days before the tournament in a practice session.

"It was obviously causing him some discomfort in the first couple of matches. He called the trainer out and he was feeling it.

"He probably would have pulled out sooner in that match last night apart from (the fact) he was on centre court, a big match on Arthur Ashe Stadium and he was kind of the name player in that match as well.

"For him to get criticised like that, he would be pretty frustrated."

Hewitt will name Kyrgios in Australia's four-man team on Tuesday, but knows from his own experiences with hip flexor injuries that the world No.16 is only a 50-50 chance of playing in the September 16-18 tie.

"We'll give him every chance to obviously get right and be fully fit," Hewitt said.

"We probably won't know a lot, though, for a few days until he gets back to Australia and really how it settles down and then we've got to weigh up whether he could maybe make the injury worse and weigh up when he can start practising.

"Then we'll have to make that decision closer to the tie whether he's going to get enough hitting on grass to be able to go out there and do a job for us, or if it's too big a risk.

"It's obviously not the best situation for us, but he'll be named."

With seemingly no plans to heed McEnroe's advice, Kyrgios is pledging to learn from his bitterly disappointing Open experience.

"This one hurts man," he posted on Twitter as he struggled to digest his first defeat in 21 matches against an unseeded player at a grand slam.

"My sights were set on some great things this week ... Not the way I wanted to end the last grand slam of the year. F**king sucks. #liveandlearn. Its only a failure if you don't learn the lesson." With Kyrgios doubtful, Hewitt is considering drafting John Millman into his squad, although Davis Cup regular Sam Groth, doubles specialist John Peers and James Duckworth remain favoured to be picked alongside singles certainty Bernard Tomic.